As Crum recalls: "We asked if we could use his office or lab to
do the measurements. But the storm went south and we couldn't
find it, so we were chasing."

What Crum and his Ole Miss colleague Ronald Roy found that trip
after rigging up acoustic equipment in a motel pool in Roanoke,
Virginia, led to a research paper published in October in the
Journal of the Acoustical Society of America. Crum, now
chair of the Acoustics and Electromagnetics Department at the
University of Washington, is the study's lead author, in
conjunction with snowchase colleague Roy, now at Boston
University, and Prosperetti.

The journal article, also co-authored by Hugh Pumphrey of the
University of Edinburgh in Scotland, reveals a bit of the
scientist's joy of discovery: Early snowfall data was "so unique
and contrary to our intuitions and expectations that it has
inspired us to accumulate data from a number of storms," the
authors wrote. After studying such data, researchers believe the
high-pitched sound Crum and Roy recorded is not caused by the
impact of the flakes but by vibrating bubbles created after the
snow hits the water's surface.

They had already detected a similar phenomenon in rainfall back
in the 1980s. Prosperetti, a wizard theorist on the relation
between bubbles and sound fields, had teamed up with Crum to
publish groundbreaking research on the role of rain-induced
bubbles in underwater noise. Among other tests, they used a
high-speed camera to capture the bubbles. This time around,
Prosperetti analyzed the acoustic signature of the snowflake
noise recorded in Virginia; he found a similar "footprint." In
both cases, the signatures revealed the typical features of
pulsating bubbles. "If it walks like a duck and quacks like a
duck, it's a duck," says Prosperetti.

It's an odd duck at that. "We think it is a bubble, but how can a
bubble be involved? A snowflake is mostly empty. It's 10 percent
water and the rest is air," Prosperetti says of the mystery. "As
a snowflake deposits itself, there is no impact essentially.
Leisurely, bumm, bumm, bumm, it drops down." A serenely
quiet scene by any standard.

"But what the layer of water engulfs is not solid ice, it is
engulfing the air of which the snowflake is made," he adds. As
water melts the ice, a bubble remains, researchers postulate.
Water surface tension and pressure then would cause the bubble to
pulsate. Those pulsations, or oscillations, create the sound.
"It's like beating a drum," Crum says.

Prosperetti (pictured at right) adds, "It's a
high-frequency sound. It would sound
like a hissing noise if we could hear it, but we can't." The
sound, ranging between 50 and 200 kilohertz, is too high for
human ears (which can normally hear nothing higher than 20
kilohertz). Snowflake screeching, which was first recorded in the
mid-1980s, adds 30 decibels to the underwater environment. "It's
the difference between a private conversation and a rock band,"
Crum says. It's unclear just how much it disturbs underwater
animals, though porpoises can hear sounds at high frequencies, he
says.

However, the noise does wreak havoc with underwater sonar
equipment.

Wildlife researchers using sonar devices to count salmon in the
Pacific Northwest, and U.S. Naval submarine officers using sonar
to detect enemy subs, dread storms because raindrops and
snowflakes have the potential to create "background noise," which
could interfere with a sub's torpedo detection. Concerns about
sonar detection gaps led the Office of Naval Research to fund
Prosperetti's and Crum's work on underwater rain noise. The
researchers suggest one possible solution: change the frequency
range of fish finders and similar sonar devices.

Their findings could lead to other applications. Scientists need
to measure rainfall in the oceans, an important factor in
studying worldwide climatology. But gathering such data is
difficult; oceans are big. Yet researchers could analyze the
signature of bubble noise picked up by remote sensors to
determine rainfall (in short, louder sound means heavier
rainfall).

The next research step in the snowflake study? Using high-speed
cameras to visually record snow bubbles. "In principle, what one
would like to see is a snowflake caught in the act," Prosperetti
points out. Trouble is, there isn't much of a practical demand
for that verification. "This stuff is nice, but it's not by
accident that there's no money in it," the veteran researcher
says.

In the end, the four-university study can't help but be a bit of
science for science's sake. Says Crum (who among other things has
climbed onto the roof of his lab on Christmas Eve to record
snowfall sounds): "When scientists get around each other and talk
about things, they don't talk about girls and cars. They talk
about how to find the next data point."--Joanne Cavanaugh Simpson

The NEAR spacecraft now in
a yearlong orbit around the asteroid
433 Eros more than 145 million miles from Earth has been named
for a man who, though he never traveled in space, launched
today's scientific passion for the study of asteroids and comets:
Dr. Eugene M. Shoemaker.

Now called NEAR Shoemaker, the NASA spacecraft designed and
operated by Hopkins's Applied
Physics Lab is exploring the
geological surface of the potato-shaped space rock in part to
look at asteroids' links to the birth of the solar system.
Shoemaker, a legendary geologist and influential researcher on
the role of asteroids and comets in the formation of planets,
died in a 1997 car accident while studying asteroid impact
craters in the Australian outback. Among other accomplishments,
Shoemaker, along with his wife and research partner, Carolyn,
helped discover the comet Shoemaker-Levy 9 that broke up and
collided with Jupiter in 1994. He taught the Apollo astronauts
about craters and lunar geology. He developed the lunar
geological time scale researchers have used to date the moon's
features. In a touching tribute last year, NASA's Lunar
Prospector spacecraft scattered his ashes on the moon.

When the NEAR mission was first being developed in the mid-1980s,
Shoemaker was part of the team. "Eros looks really old and
solid," says Carolyn Shoemaker, "and may well be a piece of a
much larger asteroid."--JCS

According to a model developed by Hopkins theoretical
neuroscientist
Ernst Niebur and verified by experimentalists,
paying attention is all a matter of neural synchrony. Niebur and
his colleagues reported their results in the March 9
Nature.
The brain is constantly flooded with sensory signals. To pay
attention to one aspect of that sensory landscape, says Niebur,
the neurons involved unite in a synchronized chorus of firing.

The senses are always "on," Niebur explains. The nervous system
is constantly feeling, smelling, hearing, and seeing. While you
are thinking about sensations in your left foot, the rest of your
body and nervous system continues to receive sensory input--about
the lighting in the room, the weight of your clothes on your
body, the odors wafting through the air. However, not all of
those sensations garner your full attention. In fact, almost all
of it gets dumped.

While Niebur is a theorist--the only one at the Krieger
Mind/Brain Institute, he collaborated with three experimental
scientists, institute neuroscientists Steven Hsiao and Kenneth
Johnson, and former postdoctoral fellow Peter Steinmetz, who is
now at the California Institute of Technology. The scientists
applied Niebur's model to data collected from testing on rhesus
monkeys.

In those studies, Johnson and Hsiao used electrodes to monitor
the activity of individual cells in a region of the monkeys'
brains containing neurons that react to touch. While the
recordings were taken, the monkeys performed tactile and visual
tasks, and switched from one type of task to another upon cue.

Previous studies had indicated that when an animal pays close
attention to a stimulus, certain neurons in the animal's brain
fire at a faster rate, perhaps two or three times as fast.

But paying attention appears to be even more complex than that,
says Niebur. The team's recent study shows that when monkeys were
paying close attention to a tactile stimulus, certain neurons in
the tactile region not only increased their firing rate, they
also fired in synchrony. When the monkeys switched to a visual
task, the degree of synchrony decreased.

While the model appears to apply to the tactile system, says
Niebur, there is no reason to believe that it would not also hold
for other sensations and even for cognition. So telling yourself
to pay close attention to your left foot probably entails an
increased degree of synchrony in a subset of your neurons.

Many questions remain. The model describes what goes on in the
brain when you are paying attention. But what starts the process?
How do we decide what to pay attention to at any given moment?

"That's a good question," says Niebur, "and we don't have all the
answers." He and his colleagues plan to conduct follow-up studies
that may provide more clues.--Melissa Hendricks

But ancient plants are preserved as fossils, and they may unlock
part of the riddle.

Jahren, along with lead author Nan Crystal Arens, assistant
professor of integrative biology at Cal-Berkeley, examined data
from 44 studies on 176 species of modern grasses and trees. They
found that the composition of plant tissue closely correlates
with the composition of the carbon in the atmosphere at the time
of the plant's life.

Says Jahren, "We believe that this will allow us to use plant
fossil composition as a proxy for ancient atmospheric
composition.

"The composition of the atmosphere is widely thought to control
the major climactic forces of the planet--that is why there is so
much concern over human activities substantially changing the
modern-day atmosphere," she continues. "By studying parts of the
Earth's history where we suspect climate change, we may be able
to better understand the link between the composition of the
atmosphere and its effect on the weather at the surface of the
planet." The study by Jahren and Arens was recently published in
Paleobiology.

Through photosynthesis, plants take in carbon dioxide from the
air. The carbon atoms in carbon dioxide vary; some are the
isotope carbon-12, and some are carbon-13, with one more neutron.
Physical and enzymatic processes within the plant differentiate
the two isotopes, allowing scientists to apply mass spectrometry
and measure the ratio of carbon-12 to carbon-13. In the 44
studies that they examined, Jahren and Arens found a strong
correlation between the ratio of the isotopes in plant tissue and
the corresponding ratio of the isotopes in the atmosphere.

These atmospheric ratios form a sort of signature, indicating the
sources of carbon in the air. Carbon enters the air from various
carbon "pools": in ancient times, these included volcanic
emissions, the weathering of carbonate rock, and emissions of gas
from the ocean floor. (Modern sources also include burning of the
biomass, such as rain forest clearing, and fossil fuel
combustion.) The carbon from each of these sources has a
different ratio of carbon isotopes. Read the ratio--examine the
handwriting, so to speak--and you can determine the source of the
carbon.

"A change in the ratio of carbon isotopes in the atmosphere
indicates a disruption in the global carbon cycle--things like
volcanic eruptions, changes in the extent of forestation, or
continental burning," says Jahren. Significant changes in the
carbon cycle, in turn, indicate major changes in climate: "Once
we can discuss changing atmosphere composition through time, we
can begin to approach what periods of carbon-cycle disruption
mean with respect to climate."--Dale Keiger

As the space century comes to a close, the cost of space missions
has climbed into the billions. NASA launched its Discovery
Program in the 1990s to reshape the culture of space science into
the lean, mean corporate model. Some of the stay-within-budget
tactics discussed at the four-day conference included employing
smaller and lighter spacecraft, satellites, and instruments;
adapting current software and other technology instead of
reinventing it; and saving travel and other costs by linking team
scientists from around the world via the Internet and
teleconferencing.

Proponents of the "leaner, meaner" philosophy touted the success
of a current APL-led mission, NEAR Shoemaker, which is now in a
yearlong orbit around the asteroid 433 Eros, at a cost of just
$216 million. But the slim-and-trim concept has its critics.
Among problems cited: a lack of thorough testing, cuts in staff
and resources (scientists who regularly work 80-hour plus weeks),
fewer risk assessment measures, and an atmosphere where speed is
a prime factor, all of which speaks to another slogan--Haste
Makes Waste.

"We can't afford as a nation to take risks with these missions,"
said Liam Sarsfield, senior policy analyst for RAND's Science and
Technology Policy Institute. "We should consider them a national
asset. I don't know what FBC [faster, better, cheaper] is. As a
slogan, I hope it goes away--the faster the better."

Tony Spear, project manager for the successful Mars Pathfinder
mission in 1997 and a NASA consultant, does not condone taking
shortcuts. But he says the overall concept is "here to stay. The
best definition, I believe, is that it's simply an attempt to
continually improve performance."--JCS